Apparatus for precise alignment and placement of optoelectric components

ABSTRACT

An apparatus and method is provided that superimposes an image of an optoelectric component on a substrate with the use of a single camera. Specifically, the camera looks through a transparent alignment tool that is holding the component, to the substrate below it, thus allowing both the component and the substrate to be seen together by the camera. The alignment tool and substrate are adjusted to precisely align the two and then are brought together while being seen by the camera. On laser chips, the chip is energized while on the glass alignment tool to produce a laser spot that is superimposed on the visible light image via a series of lenses and mirrors.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to optical and electronic bondingequipment and more particularly to bonding equipment for preciselyaligning and placing optoelectric components on substrates.

2. Description of the Related Art

Precise alignment of surfaces in the placement of optoelectriccomponents on substrates has received much attention. This isparticularly true in VLSI circuit elements where the patterning of thecircuit is microscopic or nearly microscopic. Many small components aretypically bonded to these circuits. The problem with placing these smallcomponents with high precision, i.e. within microns, is accuratelylocating and correlating the component and placement position. Also, thecomponent must be moved to the exact placement position without error.

The prior art has done this by moving the component over an uplookingvisible light camera and the substrate under a downlooking visible lightcamera. A series of pictures are taken and the two images correlated.Corrections are made by the mechanical system to place the componentover the substrate and the two are brought tog, ether. The difficulty inthis prior art is that after the component and substrate are located bythe cameras and vision system, they must be moved horizontally andvertically which introduces errors into the system. The greater thedistance the component and substrate have to move, the greater is thealignment error that results from the smallest imprecision in themechanical system's machined parts.

Another method employed is to position the component over the substrateand place a thin optical probe between them as in U.S. Pat. No.4,899,921 to Bendat et al. The mechanical system will maintain alignmentof the component and substrate for as long as the probe fits between. Atsome point the probe must be removed and the component and substratemoved together. It is at this point alignment errors are introduced.

SUMMARY OF THE INVENTION

In accordance with the principles of the invention, a transparent toolholding the component is provided. This allows a single, downwardlylooking camera to view both the component and the substrate at the sametime without having to move either the component or the substrate.Preferably, the transparent tool is formed of glass. More specifically,the component is held in place by a vacuum drawn on a capillary tubepositioned between two glass optical flats. The component is held incontact with the lower flat that incorporates the outlet for thecapillary tube. Since the entire structure is glass, the camera can lookdown directly on the component and also the substrate. Alignment andplacement are simplified as the two images of the component and thesubstrate are superimposed during the placement process. Calibration ofthe system is also simplified as there is no longer a need to calibrateimages from two different cameras. The apparatus is controlled to bringthe surfaces of the component and the substrate into desired alignmentby rotating the component and moving the bonding platform in orthogonalx, y and z directions.

This structure is particularly useful in the accurate placement ofsemiconductor laser chips on a substrate. In this configuration, thelaser chip is energized and the lasing gap is located with respect to afeature on the chip using a vision system. Usually the chip is energizedby contacting electrodes on its top and bottom. A metallization isplaced on the transparent tool surface to contact the upper surfacelaser electrode and another contacting electrode is placed on thebottom. As an alternative, the tool may be metallized with Indium TinOxide (ITHO), which is transparent and electrically conductive, or amaterial with similar properties, to function as one probe to energizethe laser. Using the transparent tool allows the surface of the laserchip to be visible for alignment purposes.

The laser is energized via the ITO portion exciting the laser to emitlight from the laser gap. Using a set of mirrors and beam splitter, theinfrared optical path used to view the light from the lasing gap isfolded into the same optic used to view the surface of the componentsallowing measurement offset for alignment correction. The folded lightemitted from the single optic is then split back into two optical paths,one infrared and the other visible light. Two cameras, one for visiblelight and one for infrared light, are used simultaneously. Thiseliminates the need for placing the laser chip in front of an infraredcamera located away from the bonding site to ascertain the positionprior to alignment.

As simplification, illuminating the laser chip with infrared and nearinfrared light, rather than in the visible spectrum, would allow theinfrared camera to capture both images, thus eliminate the need for twocameras.

As an alternative embodiment, a separate apparatus is used to correlatethe lasing gap on the laser chip with an existing feature on the chip.The visible light image used in locating and correlating the feature onthe separate apparatus is acquired using the visible light cameradescribed above. The orientation and position of the lasing gap is nowknown with respect to the substrate and the laser can now be placed withhigh precision without actually firing the laser at the bonding station.Additionally, if the tool is metallized with ITO, or similar material,as previously described, it could function as one probe to energize thelaser. The chip laser would then be positioned in front of the infraredcamera and placed in contact with a second probe by the positioningsystem, and energized. This provides the added advantage of not needingto re-acquire the visible light image by the visible light camera, andthus, eliminating the visible light camera on the separate locating andcorrelating apparatus. This, in turn, simplifies any system calibrationbetween the two pieces of apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the apparatus and method are described indetail hereinbelow with reference to the drawings wherein:

FIG. 1 is a plane view of the alignment and placement apparatusconfigured in accordance with a preferred embodiment of the presentinvention;

FIG. 1A is an expanded view of the downward looking video imagingcamera;

FIG. 1B is an expanded view of a substrate in which elements are place;

FIG. 2 is an expanded plane view of the alignment tool for use in thealignment and placement of energizable elements on a substrate; and

FIG. 3 is a perspective view of the alignment tool holding a laser chipusing mirror imaging to align to the substrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates, in a simplified manner, a preferred alignment andplacement apparatus shown generally at 10. A component 60, e.g. asilicon or laser chip, is temporarily secured to the alignment tool 20by drawing a vacuum between two flat plates 22 via hose 34. Thealignment tool 20 is of a transparent glass having a very lowcoefficient of expansion, such as Zerodur™. A video imaging camera 32(FIG. 1A) looks down through a series of optics 30 and through thetransparent alignment tool 20, to the chip 60. The depth of field ofoptics 30 encompasses both the chip 60 and the substrate 40 into thevideo image. With the chip 60 now superimposed on the substrate 40, thealignment tool 20 is adjusted using adjustment micrometers 26 and 28 tocorrect the pitch and roll angles while yaw adjustment is performed byrotary stage 33.

The substrate 40 (FIG. 1B) is securely positioned on the bondingplatform 24. The bonding platform 24 is sitting on a series oftranslational stages that move horizontally (x and y) and vertically(z). This translation and elevation is accomplished through a set ofprecision gears, air bearings and linear motors shown collectively at38. The chip 60 is aligned to the substrate 40 by adjusting thetranslational table 36 and rotary stage 33 in the x and y directionwhile being viewed through the superimposed video image in the camera32. The chip 60 and substrate 40 can be moved within microns of eachother before final alignment. Once the chip 60 is properly aligned andplanar with the substrate 40 whose plane is normal to the verticaltravel, the bonding platform 24 is raised until the chip 60 andsubstrate 40 meet and are bonded in any of the conventional bondingmethods, e.g., heat, hot gases, pressure or ultrasonic vibrations.

The alignment tool 20 of the present invention, as depicted in FIG. 2,shows in detail the holding means of the chip 60. The alignment tool 20is comprised of two parallel transparent glass plates 42 and 45,separated by an airtight spacer 46. A hole 59 is drilled vertically downthrough the lower glass plate 45 and fitted with a short length ofcapillary tube 58 so that the tube's lower surface 47 will hold the chip60. The hole 59 in the tube 58 is small enough so that the chip 60covers the entire hole 59. Drawing a vacuum in the space 44 between theupper glass plate 42 and lower glass plate 45 via hole 62 in spacer 46effectively presses the chip 60 against the end of the capillary tube47, where it remains while alignment is performed. When alignment iscomplete, the chip 60 and substrate 40 are brought together and the chip60 is bonded on the bond pad 64. The vacuum is then relieved. Videocamera 32, using optic 30, will look down through the transparentalignment tool 20 and capture an image combining views of the chip 60and substrate 40 with bond pad 64. To further aid in aligning the chip60 with the bond pad 64, fiducials may be placed on the chip 60 and thesubstrate 40 to facilitate placement. Alternatively, other features ofthe chip 60 may be used. The edges are normally not used as they arevery sensitive to lighting changes and are prone to chipping.

As an addition to this embodiment, if chip 60 is a semiconductor laserchip, as shown in FIG. 3, and must be aligned to another opticalcomponent, such as an optical fiber or ball lens, with very highprecision, the capillary tube's lower surface 47, which holds the laserchip 60, is metallized with ITO or some other suitable substance, sothat it may be used as one contact to energize the laser chip 60. Theenergized laser chip 60 emits light from its lasing gap 66 forming alaser spot on a facet 67 of the laser chip 60. The laser spot 66, withrespect to the other optical component, is used as a further means toalign the laser chip 60 to the substrate 40. Once the laser chip 60 hasmade contact with the metallization at 52, by drawing the vacuum, it isthen positioned in contact with a probe (not shown) as the secondelectrical contact to energize the laser chip 60. The laser spot 66 isthen referenced to a feature such as the fiducials 54 on the top of thelaser chip 60. The information regarding the position of the laser spot66 is then correlated to the image of the substrate 40 and the component43, and the laser chip 60 is aligned at the proper location for bonding.

As a further embodiment to the basic preferred embodiment, FIG. 3 showsa perspective view of the alignment tool 20 holding a laser chip 60using mirror imaging to align to the bond pad 64 on the substrate 40.The glass alignment tool 20 is metallized 48 to provide a circuit toenergize the laser chip 60 while being held by vacuum through thecapillary tube 58 to the alignment tool 20. It should be noted thatthese metallizations may be of any suitable material, including ITO andthat the metallization location is dependent on the position of theconnecting wire bond pads 50 on the laser chip 60. The circuit iscompleted at the electrical contacts 52 with the wire bond pads 50 onthe laser chip 60. The energized laser chip 60 produces a laser spot 66.This spot 66 is collimated by a first lens 68, deflected ninety degreesby a first mirror 70, deflected a further ninety degrees by a secondmirror 72, refocused by a second lens 74 and then directed upwards by abeam splitting lens 76. This final image of the spot 66 is superimposedon the visible light image 56 of the top of the laser chip 60 whichpropagates through the alignment tool 20. Visible light camera 32 isreplaced with an infrared camera and laser chip 60 is illuminated withan infrared source for viewing its top. The combined image 78 is nowcaptured and analyzed. Alignment adjustments are made to the laser chip60 and substrate 40 before the substrate 40 is raised to the laser chip60 and bonded. Position correction information is determined from thesingle combined image 56 of the laser spot 66 and the bond pad 64. Thefiducials 54 are used as a secondary means of alignment with the laserspot 66. Due to the refractive index of the tool material being greaterthan air, some calibration is required clue to the apparent and actualimages of the top of the laser chip 60 being offset.

Although the subject invention has been described with respect topreferred embodiments, it will be readily apparent to those havingordinary skill in the art to which it appertains that changes andmodifications may be made thereto without departing from the spirit orscope of the subject invention as defined by the appended claims.

What is claimed is:
 1. An apparatus for alignment and placement of acomponent on a substrate having a substrate support means for supportingsaid substrate thereon, said substrate configured to receive saidcomponent, comprising:tool means for aligning and placing said componenton said substrate, including a substantially light transparent portionand an electrically conductive portion configured to selectivelyenergize said component to emit light; and an image gathering opticssystem including at least one camera positioned relative to said toolmeans and said substrate for receiving positional information regardingsaid component and said substrate through said light transparent portionwhile said component is secured to said tool means by a holding means.2. The apparatus of claim 1 wherein said substrate support means is abonding platform moveable in the x, y and z axes.
 3. The apparatus ofclaim 1 wherein said tool means is moveable in pitch, row and yawangles.
 4. The apparatus of claim 4 wherein said electrically conductiveportion comprises an Indium Tin Oxide strip.
 5. The apparatus of claim 1wherein said camera is positioned directly above said tool means andsaid substrate.
 6. The apparatus of claim 1 wherein said holding meansis a plurality of transparent optical flat plates, at least one having acapillary tube in contact with said component forming a vacuum betweensaid plurality of transparent optical flat plates and through saidcapillary tube, holding said component to said tool means.
 7. Theapparatus of claim 6 wherein said transparent optical flat plates areglass.
 8. The apparatus of claim 1 further comprises an optical systemfor relaying further positional information to said camera regardingsaid component when said component is energized to emit said light. 9.The apparatus of claim 8 wherein said tool means further comprises anelectrode contacting said component, together with said electricallyconductive portion of said tool means allowing said component to beenergized to emit said light.
 10. The apparatus of claim 9 wherein saidlight is infrared laser light.
 11. The apparatus of claim 10 whereinsaid infrared light is superimposed on a white light image of saidcomponent and reflected to said image gathering optics system.
 12. Theapparatus of claim 11 wherein said reflection being from a combinationof reflective mirrors and collimating lenses.
 13. An apparatus foralignment and placement of an optoelectric component on a substratehaving a substrate support means for supporting said substrate thereon,said substrate configured to receive said optoelectric component,comprising:tool means for aligning and placing said optoelectriccomponent on said substrate, including a substantially lighttransmissive portion, a plurality of electrically conductive portions asa plurality of electrical contacts to selectively energize saidoptoelectric component, creating a laser spot on said optoelectriccomponent, and a means to energize said optoelectric component; holdingmeans for temporarily securing optoelectric component to tool means,including a plurality of transparent optical flat plates horizontallylayered, the lowest of said transparent optical flat plates having asmall bore vertically down to a capillary tube forming a vacuum on saidcapillary tube to said bore and through a spacing between said layers ofsaid flat plates, allowing said optoelectric component to be held totool means; and an image gathering system including a plurality ofcameras for correlation and calibration including at least one whitelight camera positioned relative to said tool means and said substratesupport means for receiving positional information regarding saidoptoelectric component and said substrate through said lighttransmissive portion of said optoelectric component and at least oneinfrared camera positioned relative to said tool means and saidsubstrate support means for receiving positional information regardingsaid laser spot on said optoelectric component, a probe contacting saidoptoelectric component aiding in energizing said optoelectric component,and a calibration means to correlate and mathematically evaluate aplurality of images from said at least one white light camera and saidat least one infrared camera.
 14. The apparatus of claim 13 wherein saidimage from said at least one white light camera entails a feature fromsaid optoelectric component.
 15. The apparatus of claim 13 wherein saidsubstrate having at least one fiducial thereon aiding in alignment ofsaid optoelectric component.
 16. The apparatus of claim 13 wherein saidimage gathering system further comprises a plurality of reflectivemirrors and collimating lenses aiding said plurality of cameras inreceiving positional information.
 17. The apparatus of claim 13 whereinsaid plurality of electrically conductive portions comprise Indium TinOxide.